Telephone-transmitter.



No. 845,062. PATENTED FEB. 26, 1907. J. M. DEMPSEY.

TELEPHONE TRANSMITTER.

APPLICATION FILED NOV. 30, 1906.

I9 20 4 Z4 Z7 THE NORRIS PETERS co., \VASHINGTDN, a. c.

UNITED STATES PATENT OFFICE.

JAMES MICHAEL DEMPSEY, OF CHICAGO, ILLINOIS, ASSIGNOR OF THREE- TENTHS TO WILLIAM B. BECKMAN, OF FAYETTEVILLE, ARKANSAS, AND THREE-TENTHS TO HARRY T. ROGERS AND ONE-TENTH TO MADELINE DEMPSEY, BOTH OF CHICAGO, ILLINOIS.

TELEPHONE-TRANSMITTER.

Specification of Letters Patent.

Patented Feb. 26, 1907.

Application filed November 30, 1906. Serial No. 345,718.

To all whom, it may concern:

Be it known that I, JAMES MICHAEL DEMP- SEY, a citizen of the United States of America, and a resident of Chicago, in the county of Cook and State of Illinois, have invented certain new and useful Improvements in Telephone-Transmitters, of which the following is a specification.

This invention relates to telephone-transmitters, and has particular reference to transmitters and microphones in which sound is transmitted by means of an electric circuit whose resistance is varied through variations of pressure exerted upon a yielding mass of conducting material, such as carbon granules, which is included in the circuit and connected with a diaphragm so as to receive vibrations therefrom.

The main objects of this invention are to provide an improved form of telephone transmitter capable of transmitting and intensifying sounds and wherein a slight vibration of the diaphragm will exert a powerful efiect upon the resistance of the electric circuit which transmits the sound to a distant receiving instrument, to provide a form of telephone-transmitter which is capable of transmitting sounds originating at considerably greater distances from the diaphragm than is possible with the usual forms of telephone instruments, to provide a construction which will require a minimum strength of current for its operation and which is free from rubbing parts which introduce sounds foreign to the voice of the speaker, and to provide means which inay be readily operated from the outside of the transmitter for preventing the packing of the carbon granules, thereby insuring long continued efliciency of the apparatus without readjustment. These objects are accomplished by the device shown in the accompanying drawing, which represents a horizontal section through a transmitter constructed according to this invention.

In the form shown in the drawing the transmitter comprises a casing 1, having an opening 2 in its front wall fitted with a mouthpiece 3. The diaphragm 4, preferably of thin mica or other material, which is delicately sensitive to sound-waves, is mounted in the usual packing-ring 5 and extends across piece 8, which extends across the interior of the casing. The cell 6 is mounted on the bridge-piece 8 so that it may be adjusted toward and away from the diaphragm. A stirring-fork 9, preferably of glass or other nonconducting material, is embedded within the mass of carbon granules and has a shank 10 extending outward through the shank 11, which supports the cell 6. Said shank 10 is provided with an arm 12, extending outward through a slot in the casing, so as to permit of moving the fork for stirring the granules occasionally, so as to prevent them from becoming packed and losing their sensitiveness to variations in pressure.

The end of the cell 6 which is away from the diaphragm 4 is closed by means of a thin mica disk 13, whose connection with the walls of the cell are sealed in the usual manner, so as to prevent the entrance of moisture into the cell. The disk 13 carries the usual electrodes 15 and 16, which form part of the primary circuit, the conductors connected to said electrodes being indicated at 23. The mica disk insulates the electrodes 15 and 16 from each other, and current can pass from one to the other only through the mass of carbon granules which is in contact with both electrodes. The resistance of the carbon granules varies with the pressure thereon. A post 14 is rigidly connected in the middle of the disk 13 and is pointed at its outer end. A lever 24, which is fulcrumed on a knife-edge 17 on the casing, bears upon the post 14, the point of said post being seated in a conical socket in the lever. The lever 24 extends to a position directly opposite the center of the diaphragm 4, and the vibrations of the diaphragm 4 are communicated to the lever 24 by means of a spindle 18, which preferably has pointed ends seated in conical sockets respectively mounted upon the diaphragm and the lever 24. The spring 19, which is fastened to the casing, bears upon a pin 20 on the lever 24 and through said lever exerts an initial compression upon the carbon granules in the cell 6. The amount of this compression is adjustable by means of a set-screw 21,

bearing between the casing and the spring 19. The post 14, the spindle 18, the fulcrum 17, and the sockets which engage them are all hardened, so that the connections between the various moving parts may be line point or line bearings, thus eliminating friction and the rubbing of parts Which would be caused it said connections were pivoted In adjusting the device the desired initial compression upon the carbon granules is obtained by means of the set-screw 21. The socket 22 in the lever 24: is preferably adjusted so that a slight outward. pressure will be exerted upon the diaphragm l, thus avoiding any looseness in the connections.

'lhe operation of the device shown. is as follows: 'lhe sound-waves enter the mouthpiece 3 and strike the dia hrag1n 4, causing the same to vibrate. The advancing movement of each soundqvave presses the diaphragm inward, the reverse move nent ol the diaphragm being due to its res 'ence. In this device the inward movement of the diaphragm reduces the pressure upon the carbon granules instead of increasing such prssure, as is usually done in electric telcplmne-transmitters. 'lhe inWard movement c1 the diaphragm is therefore resisted only by the yielding spring instead of by the comparatively uny ielding mass of carbon. The lever transmits to the carbon granules vibrations of reduced amplitude, but of greater intensity than those of the (.liaplnagm, that the carbon granules have less etl'ect in resisting or dampening the vibration of the diaphragm than is usual, thus rendering said diaphragm much more eilective in. transmitting sound. "he initial compression upon the carbon granules causes them to oil'er comparatively little normal resistance to the flow of current between the electrodes 15 and 16 and makes it possible to operate the herei inde scrib e d transmitter under much less current than is necessary in. the ordinary devices.

'Ihe lever as herein applied gives to Weak sounds the power to cause much. more eileotive variation in the pressure upon the carbon granules than i'l the diaphragm Were resisted. directly by the carbon, as in the usual form of transmitter.

By agitating the stirring device from time to time the carbon granules are prevented. from becoming packed, and the device is therefore capable of always being kept in an ei'licient state.

What I claim as my invention, and desire to secure by Letters Patent, is

1. A transmitter comprising a diaphragm arranged to be sensitive to sound-Waves, a cell containing a quantity ol granular conducting material, a spring arranged to exert an initial compression. upon the material in said cell, an electric circuit including said granular material, and means interposed bel l i tween said diaphragm and said spring and adapted to reduce the pressure on said materi l through a movement of said diaphragm in the dirction ol the advance of sound- Waves str'king it.

2. A transmitter comprising a diaphragm arranged to be sensitive to sound-waves, a cell containing a quantity ol granular conducting material, a spring arranged to exert an initial compression upon the material in sa d cell, an electric curouit including said granular material, and means interposed between said diaphragm and said spring and adapted to reduce the pressure on said material through a movement of said diaphragm in the direction ol the advance ol' sound- Waves strlk=ng it, said means being adapted to transmit to said granular material vibrations of greater intensity than the vibrations of the diaphragm itsell.

3. A transmitter comprising a casing bar 3 ing an opening at one side, a diaphragm stretched across said opening and adapted to be vibrated. through sound-Waves entering said opening, a cell containing a quantityoi' granular material mounted in said casing in- W d of the diaphragm, a spring arranged to exert an initial compression upon said granular material, an electric circuit including said granular material and adapted to have its resistance varied through a variation in the pressure on said material, a lever lull-ruined in. said casing and arranged to be oscillated through the vibrations oi said diaphragm, said lever having an arm acting on said granular material and adapted to release the pressure upon said material through an inward movement of said diaphragm, means for adjusting said spring to alter the ini in! pressure upon. said material, and an adjustment between said lever and diaphragn'i to prevent lost motion through changes in the adjustment of said spring.

t. A transmitter comprising casing having an opening at one side, a diaphragm mounted at said opening and adapted to be vibrated through sound-Waves entering said opening, a pair oi electrodes, a quantity ol granular conducting material in. circuit with said electrodes, a spring exerting an initial compresson upon said granular material, means interposed between said ditphragm and spring W hereby said spring normally urges the d laphragm outwardly of said opening and whereby the inward movement of said diaphragm causes a variable reducthm in the pressure of said spring upon said granular material.

Signed at Chicago this 28th day ol Novemher, 1906.

JAMES MICHAEL DEMPSE 1". Y'Vitnesses E. A. RUMMLER, NM. R. RUMMLER.

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